1. Field of the Invention
The present invention relates to a rolling bearing with a built-in motor which can be used in a drive apparatus for driving a robot, industrial automated equipment, computer equipment and its peripheral equipment. The present invention also relates to a distributing actuator which is used in a semiconductor manufacturing apparatus and in an industrial robot.
2. Description of the Related Art
As a direct drive motor which is used in the field of factory automation (FA), for example, there is known one disclosed in JP-A-63-213457 having a structure shown in FIG. 44. This direct drive motor uses a crossed roller bearing 110 as the bearing of the motor and, in the interior portion of the bearing, there are held, via a housing 112, an encoder 114 on the inner side in the radial-direction thereof and a stator 116 on the axial direction thereof. A rotor 120 and a slit plate 122 included in the encoder 114 are fixed to the outer portion of the bearing, through a rotor hub 118. And, the rotor hub 118 can be rotated by receiving the drive force of a motor which is composed of the rotor 120 and stator 116.
Now, FIG. 45 shows the structure of an exciting coil disposed on the stator 116. Here, there is used an exciting circuit having three phases (A phase, B phase, and C phase). The stator 116 includes a plurality of salient poles 124a–124l which are projected radially from the stator 116; and, poles are formed by winding conductors around the respective salient poles. Specifically, the A phase is wound on every third salient poles, that is, a total of four salient poles 124a, 124d, 124g, 124j in series; the B phase is wound on the four salient poles 124b, 124e, 124h, 124k in series; and, the C phase is wound on the four salient poles 124c, 124f, 124i, 124l in series. By the way, the position relationship between teeth respectively formed on the mutually opposed surfaces of the stator 116 and rotor 120 is similar to a PM (Permanent-magnet Motor)-type pulse motor.
Now, FIG. 46 is an explanatory view of the rotation principle of the rotor 120.
The magnetic flux to be produced by the salient poles of the stator 116 can be expressed as the sum of a bias magnetic flux φM produced by a permanent magnet and a excitation magnetic flux φC produced by conducting an exciting current through an exciting coil wound on a salient pole, that is, φO=φM+φC. Here, in case where the current is conducted through the exciting coil while allowing the salient poles to have a phase difference of 120° in the order of A phase—B phase—C phase, the excitation magnetic flux φC moves in the order of A phase—B phase—C phase, so that the magnetic flux portion of φO is caused to move. For this reason, the rotor 120 is attracted to this magnetic flux portion to thereby be able to produce a rotation drive force in the rotor 120.
Also, as a second example of the conventional direct drive motor, there is known one which is disclosed in JP-A-62-68455U having a structure shown in FIG. 47. This direct drive motor uses a crossed roller bearing 110: specifically, a stator 138 is fixed to a frame 126 connected to the outer ring of the bearing; a rotor 130 is disposed on the side of a shaft in such a manner that it is opposed to the inside diameter side of the stator 138; and, on the inner side of a shaft to which the rotor 130 is to be fixed, there is disposed a detector device 132 for detecting the position and speed of the rotor 130.
Further, as a third example of the conventional direct drive motor, there is known one disclosed in JP-A-9-56108 which is used in computer equipment. In this publication, there is disclosed a composite bearing apparatus having the following structure. That is, the composite bearing apparatus includes a two-step shaft including a large-diameter portion and a small-diameter portion, balls are interposed between an outer peripheral rolling groove formed in the inner peripheral surface of an outer ring and an inner peripheral rolling groove formed in the outer peripheral surface of the large-diameter portion of the two-step shaft, and further balls are interposed between an inner peripheral rolling groove formed in an inner ring fitted with the small-diameter portion of the two-step shaft and an outer peripheral rolling groove formed in the inner surface of a sleeve outer ring. And, a rotor and a stator are disposed on the outer periphery side of the sleeve outer ring of the composite bearing apparatus.
However, in all of the above-mentioned conventional structures, the rotor and stator cooperating together in forming the drive source as well as the detector are disposed in the interior portion of the motor separately from the bearing and, therefore, due to the installation space for these parts, it is difficult to reduce the size of the bearing apparatus. Specifically, in the case of the structure disclosed in JP-63-213457, the rotor 120 and stator 116 are disposed next to the crossed roller bearing 110 in the axial direction thereof, and the detector device (encoder) 114 is disposed on the inner side of the diameter direction of the crossed roller bearing 110; and, in the case of the structure disclosed in JP-62-68455U, the detector device 132 is stored in the diameter-direction inner portion of the rotor 130. These structures can reduce the axial-direction length of the roller bearing, which can reduce the size of the roller bearing to some degrees. However, in these structures, in fact, the size reduction is not sufficient. Also, such compact structure complicates the whole structure of the bearing and motor, increases the number of parts and complicates the process for assembling the parts into the roller bearing, which results in the increased manufacturing cost of the roller bearing. Further, it is difficult to provide a proper degree of rotation accuracy with respect to the shaft in assembling, which makes it difficult to assemble the rolling bearing with a sufficient degree of accuracy.
And, in the case of the structure disclosed in JP-A-9-56108, since the rotor and stator are disposed on the outer periphery side of the composite bearing, it is also difficult to reduce the size of the composite bearing.
In addition, a conventional rotation drive apparatus to be incorporated into the joint portion of an industrial robot is structured such that, for example, the motor shaft of an electric motor and a rotation drive shaft are connected together by a coupling and the rotation of the electric motor is transmitted to the rotation drive shaft through the coupling. Due to this, the rotation drive apparatus requires a bearing and the coupling for supporting the rotation drive shaft, which in turn requires a space for installation of these component parts. However, this space makes it difficult to reduce the size of the rotation drive apparatus.
In view of this, in JP-A-1-144369, there is disclosed a rotation drive apparatus of a direct drive type in which, an ultrasonic motor is used as a motor for driving a rotation drive shaft, and the rotation drive shaft can be driven directly by the ultrasonic motor. This rotation drive apparatus eliminates the need for provision of the above-mentioned coupling and thus does not need to secure a space for installation of the coupling, thereby being able to reduce the size of the rotation drive apparatus.
However, in the rotation drive apparatus disclosed in the above publication, since the vibrating body of the ultrasonic motor is contacted with the inner ring of the bearing for supporting the rotation drive shaft to thereby drive the rotation drive shaft, there is a possibility that there can occur slippage between the inner ring of the bearing and the vibrating body. Due to this, in the above-mentioned conventional rotation drive apparatus, although the size of the apparatus can be reduced, the drive efficiency of the rotation drive shaft is low.
Further, as a motor which is capable of rotating a driven shaft without using a coupling, JP-A-6-276717 discloses a bearing motor as shown in FIG. 48.
A bearing motor shown in FIG. 48 comprises the following parts: that is, a circular-collar-shaped main stator 410; two collar-shaped guide plates 406; a cylindrical-shaped spacer 407; balls 408; two circular-collar-shaped permanent magnet plates 405; two coils 404; and, two circular-collar-shaped auxiliary stators 401.
The main stator 410 comprises two circular-shaped main magnetic poles 411 each including not only two circular-shaped ball rolling grooves respectively formed in the upper and lower surfaces on the inner periphery side thereof but also a plurality of pole pieces arranged radially on the outer side thereof. The guide plates 406 are respectively disposed opposed to the ball rolling grooves of the main stator 410 and include circular-shaped ball rolling grooves corresponding to the ball rolling grooves of the main stator 410. The cylindrical-shaped spacer 407 is inserted into an insertion hole formed in the main stator 410 for supporting and fixing the inner peripheral sides of the guide plates 406 and also supports and fixes a driven shaft B inserted into the main stator 410. The balls 408 are interposed between the ball rolling grooves of the main stator 410 and the ball rolling grooves of the guide plates 406.
Each of the permanent magnet plates 405 includes a circular-shaped magnet member having vertically magnetized and radially arranged magnet pieces, the number of which is the same as or different from that of the pole pieces of the main magnetic pole 411. And, the permanent magnet plates 405 are respectively arranged opposed to the main magnetic poles 411 with their respective inner peripheral sides fixed to their associated guide plates 406. The two coils 404 are respectively disposed on the upper and lower surfaces of the outer peripheral side of the main stator 410. Each of the auxiliary stators 401 includes a circular-shaped auxiliary magnetic pole 402 having pole pieces arranged radially on the inner peripheral surface thereof, the number of which is the same as that of main magnetic pole 411. And, the auxiliary stators 401 are situated outside in the thickness direction of the coils 404 and permanent magnet plates 405 and respectively fixed to the upper and lower surfaces of the main stator 410 with their respective auxiliary magnetic poles 402 opposed to their associated main magnetic poles 411.
Since the above conventional bearing motor can transmit the output of the motor directly to the driven shaft B, the coupling can be omitted. However, there still remain the following problems to be solved. That is, in the bearing motor, a rotor is composed of the permanent magnet plates 405, guide plates 406 and spacer 407; a stator is composed of the main stator 410, coils 404 and auxiliary magnetic poles 402; and, a bearing mechanism is composed of the balls 408 and guide plates 406. This structure is large in size in the radial and axial directions thereof.
Conventionally, a distributing actuator for use in a semiconductor manufacturing apparatus includes, for example, a distributing element and a drive mechanism for driving the distributing element in the vertical direction, in the horizontal direction, or in the back-and-forth direction.
Although the above conventional distributing actuator is able to feed a substrate such as a wafer to a target place, it also have the following problems to be solved. That is, in the conventional distributing actuator, since there are required drive motors the number of which corresponds to the driving directions of the distributing element, the structure of the distributing actuator is complicated and the manufacturing cost thereof is expensive.